|Publication number||US7308243 B2|
|Application number||US 10/633,696|
|Publication date||11 Dec 2007|
|Filing date||5 Aug 2003|
|Priority date||17 Apr 2003|
|Also published as||US20040209589|
|Publication number||10633696, 633696, US 7308243 B2, US 7308243B2, US-B2-7308243, US7308243 B2, US7308243B2|
|Original Assignee||Nokia Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Classifications (12), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
The invention relates to a mixer arrangement and, in particular but not exclusively, to a mixer arrangement for use in a base station or mobile station or similar entity in a wireless telecommunications network.
2. Description of the Related Art
An area covered by a cellular telecommunications network is divided into a plurality of cells. Each of the cells has a base station arranged to transmit signals to and receive signals from mobile stations in the cell associated with the respective base station. Mobile stations will be in active communication with the base station associated with the cell in which the mobile station is located.
Both mobile stations and base stations take signals which are at a base band frequency and up convert them to a radio frequency for transmission. The base band frequency signals are either directly converted to the radio frequency or are converted via one or more intermediate frequencies. In order to up convert the base band frequency to the radio frequency directly or via the intermediate frequency or frequencies, a mixer is used. The mixer receives one input from the signal to be up converted and a second input which includes a frequency component. The second input to the mixer is generated by a local oscillator. The mixer mixes the two inputs and the resulting signal output by the mixer will have the signal information contained in the first input and will be at a frequency which is typically the sum of the input frequencies. For example, if a signal which is to be up converted has a frequency A (first input) and the signal with which it is to be mixed has a frequency B (second input), the mixer will output a frequency of A+B (or A−B in some implementations).
However, mixers which are used for this purpose have the problem that they allow the input signals to feed through the mixer. This means that the mixer will output the A+B frequency signals but also the signal at frequency A and the signal at frequency B. This can be a problem in that the frequency B is generally much greater than frequency A so that B is relatively close to the frequency A+B. Accordingly, in order to remove the unwanted B frequency, other devices have used complicated filtering solutions. For example, surface acoustic wave (SAW) filtering may be used which is both expensive and complicated to implement.
If the unwanted signal at frequency B is not filtered, this can lead to more harmful intermodulation products that can fall within the band of the wanted output. This produces loss of performance in the transmitter as the spectral purity is degraded. The unwanted local oscillator amplitude can drive some of the following power amplifier stages into compression which in turn produces more unwanted non linearity problems.
New standards are being proposed and implemented which involve using wide band multi carrier systems. It has been found that the problem of the unwanted frequency feeding through the mixer has a significant impact on such systems and can limit their performance.
The invention addresses one or more of the problems discussed above.
According to an embodiment of the invention, there is provided a mixer arrangement. The mixer arrangement includes a first mixer having at least one signal input for receiving a first signal the frequency of which is to be changed, at least one frequency input for receiving an input frequency and at least one output, the first mixer being configured to mix a first signal with an input frequency to provide an output which is output by the at least one output a second mixer having at least one frequency input for receiving an input frequency and at least one output, at least one output of the first mixer and at least one output of the second mixer being combined to cancel unwanted components from the input frequency in the outputs of the mixers.
For a better understanding of the invention and as to how the same may be put into effect, reference will now be made by way of example only to the accompanying drawings in which:
Reference is made to
Reference is made to
It should be appreciated that the arrangement shown in
Reference is now made to
The received signal is converted from a digital signal to an analog signal by a digital to analog converter 26. The output of the digital to analog converter is input to an amplifier 28 which amplifies the signal. The amplified signal is input to a mixer 30, which also receives an input from a local oscillator. The mixer 30 up converts the base band frequency to the radio frequency. The output of the mixer 30 is input to a band pass filter which removes unwanted frequency components. The output of the band pass filter is input to a power amplifier 34 which amplifies the signal. The signal is then transmitted by an antenna 36.
It should be appreciated that the number and/or position of band pass filters as well as amplifiers is again a matter of design choice. Accordingly, more or less than the two power amplifiers shown in
Reference is now made to
Reference is made to
Reference is now made to
The first mixer 52 has a first output 66 and a second output 64.
The second mixer 54 has a first input 68 and a second input 70. The first and second inputs 68 and 70 are connected to each other via a resistor 80 or other suitable resistive element. This resistor 80 has a resistance which is similar to the resistance on the first input 56 to the first mixer 52. It should be appreciated that the same resistance will in fact also be on the second input 58 the first mixer. In alternative embodiments of the invention, the inputs may be connected to ground. This may or may not be via a resistor.
The second mixer 54 has a third input 72 which receives the output 88 of the local oscillator. Finally, the fourth input 74 to the second mixer 54 is arranged to receive the inverted output 86 of the local oscillator. It should be appreciated that the local oscillator output 88 and the inverted local oscillator output 86 are input to both of the mixers.
The output of the second mixer is provided by outputs 76 and 78.
The first output 66 of the first mixer 52 is connected to the second output 76 of the second mixer 54 at a common node 84 which provides a single output signal. The second output 64 of the first mixer 52 is connected to a node 82 which is also connected to the first output 78 of the second mixer 54. The node 82 provides an output signal which is the inverse of the output signal provided by node 84.
Reference is now made to
The inputs to the first mixer 52 are at frequency A which is either an intermediate frequency or a base band frequency. The frequency provided by the local oscillator is a frequency such that when frequency B is mixed with frequency A, for example added or subtracted, the resulting signal will be at a higher intermediate or radio frequency depending on the design of the base station.
Consider an example of down conversion: A=910 MHz and B=900 MHz. The wanted frequency A−B=10 MHz and the unwanted frequency is A+B=1810 MHz. In a receiver according to this example where A−B, B, and A+B are far apart, the problem is not so great. The difficulty is that the unwanted frequency B can be very large in amplitude relative to the small wanted frequency at A−B and can cause difficulties such as saturating amplifier stage and causing distortion. Hence it is good to eliminate it at source, which can be performed by this invention.
The mixer will also down convert the image frequency at 890 MHz to the same frequency as A−B, i.e. Image A=890 MHz, B=900 MHz, and A−B=10 MHz. It lands on 10 MHz but with a phase shift, this can be removed by filtering the image at 890 MHz and then using image rejection mixers to further reduce this.
Embodiments of the invention can be embedded into an image rejection mixer. The image frequency is any unwanted signal at that frequency. It may be just low level noise, intermodulation distortion products from some other system, an alien blocker trying to jam your communications system and/or sidebands from the same transmitter, or the like.
By connecting the output of one of the mixers to the output of the other mixers, the local oscillator components can be cancelled. The first output 66 of the first mixer which provides an output with an unwanted frequency component B and a wanted frequency component A+B (both components are non inverted) is connected to the same node 84 as the output of the second mixer 54 which contains the unwanted component at frequency component from the inverted local oscillator signal. By connecting these two outputs together, the unwanted components from the local oscillator are removed to just provide the wanted component—that is the signal at frequency (A+B) MHz. Likewise, by connecting the second output 64 of the first mixer, which contains the unwanted component from the inverted output of the local oscillator and wanted component of the signal at frequency (A+B) MHz which is inverted to the output 78 of the second mixer, which provides the non inverted component from the oscillator, unwanted oscillator components are 180 degrees out of phase so when added together they simply cancel each other out. This just leaves the inverse of the desired component of the output, that is (A+B) MHz. This is shown in
It should be appreciated that in the embodiments of the invention, a single local oscillator provides all of the local oscillator signals for the mixers. In alternative embodiments of the invention, the local oscillator can be replaced by any other suitable frequency source.
Reference is made to
Embodiments of the invention have been described in the context of a base transceiver station. However, it should be appreciated that embodiments of the invention can also be used with a mobile station or indeed any other communications entity.
It should also be appreciated that embodiments of the invention have much wider application than to telecommunications and can be used in any situation where a signal needs to have its frequency changed.
The aforementioned embodiments of the invention have been described in the context of radio frequency signals. However it should be appreciated that embodiments of the invention can be used with a wide range of frequencies some of which can be lower than radio frequency signals and other of which may be higher.
Embodiments of the invention have been described in the context of the up conversion of a signal. It should be appreciated that embodiments of the invention can also be used where down conversion of a signal is required.
It should be appreciated that embodiments of the invention make direct conversion that is where a signal is converted from base band frequency to the radio frequency directly without going via an intermediate frequency.
Embodiments of the invention are particularly suited to integrated circuit integrated technologies. Accordingly, the embodiments of the invention are implemented on an integrated circuit. However, it should be appreciated that embodiments of the invention may be also implemented with discreet components.
Embodiments of the invention have the advantage that implementation is simple. Embodiments of the invention may eliminate the need for complex filtering. Additionally wide band multi carrier systems can be more readily achieved if embodiments of the invention are used.
Because embodiments of the invention use two signal paths which are well matched, particularly if embodiments of the invention are implemented in integrated circuitry, the need for complex gain and phase adjustment circuitry can be removed. Although two mixers are required, generally mixers require relatively small amounts of silicon area and indeed the amount occupied by the additional mixer is probably considerably less than the more complicated filtering that would be required. Additionally, it is much easier simply to have two duplicate mixers than to provide the complex additional filtering circuitry that would otherwise be required. Furthermore, the mixers are passive circuit elements and have very little power consumption and all thus much more efficient than more power hungry circuitry that might otherwise be required if embodiments of the invention were not used. Because embodiments of the invention allow up conversion to be done in one step or two steps relatively easy, the more complicated up conversion schemes of conventional mixer arrangements involving two or even more steps can be avoided.
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|GB2236225A *||Title not available|
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|U.S. Classification||455/323, 455/302, 455/313, 455/314|
|International Classification||H04B1/26, H03D7/14|
|Cooperative Classification||H03D7/18, H03D7/1458, H03D7/1483, H03D7/14|
|European Classification||H03D7/14C2, H03D7/14|
|3 Feb 2004||AS||Assignment|
Owner name: NOKIA CORPORATION, FINLAND
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:DORNING, PHILIP;REEL/FRAME:014956/0617
Effective date: 20031130
|18 Jul 2011||REMI||Maintenance fee reminder mailed|
|11 Dec 2011||LAPS||Lapse for failure to pay maintenance fees|
|31 Jan 2012||FP||Expired due to failure to pay maintenance fee|
Effective date: 20111211